Strength Of Base Metal Research Articles

Microstructure and properties of Cu/Ti laser welded joints

Microstructure and properties of Cu/Ti laser welded joints. The optical microscopy, SEM, EDS, XRD and TEM were applied to assess the microstructure and bonding mechanism of Cu/Ti joints. When the laser beam was used to irradiate the copper side with an offset value of 0.45 mm, the welded metal and fusion line of Cu side were mainly consisted of the Cu solid solution. The intermetallic layer was formed at the titanium-welded metal interface. The thickness of IMCs was about 25 μm and consisted of the Cu solid solution, intermetallic compounds such as TiCu, TiCu2, Ti2Cu and Ti3Cu4. The tensile strength of butt joints could reach 151 MPa, i.e. 61% of the tensile strength of the copper base metal. The quasi-cleavage fracture occurred at the IMCs.

Influence of Water Cooling and Post-Weld Ageing on Mechanical and Microstructural Properties of the Friction-Stir Welded 6061 Aluminium Alloy Joints

A 6061-T6 aluminium alloy was friction stir welded in submerged water as well as in air cool at a constant traverse speed and different rotational speed in order to investigate the microstructural characterization and mechanical behaviour of the joints. In order to improve the tensile strength of the joints, weldments were studied at different heat treatment processes such as post weld aged condition and solutionized condition. It is observed that, water cooled joints are resulted in enhancing of both strength and ductility with the lower strain hardening ability than the air cooled joints. The width of the hardness distribution varies with the different cooling process of the joints. The highest hardness peak observed to be located in the heat affected zone of the joints. The maximum tensile strength of the joints achieved for welds under water cooled conditions in contrast to air cooled conditions. Moreover, a combination of water cooling and post weld ageing is proven to be the optimal path to improving the microstructural and mechanical properties of the joints with a maximum efficiency of 89.87% of the base metal strength. The microstructural observations of the joints revealed the presence of voids defects for the low rotational speed joints due to the insufficient heat input. The nugget of the higher tensile strength joints were free from defects and showed the fine grained material flow patterns which are constructive to obtain better mechanical properties.

Effect of thermomechanical parameters on mechanical properties of base metal and heat affected zone of X65 pipeline steel weld in the presence of hydrogen

In this study, the effect of different microstructures resulting from thermochemical processes of X65 pipeline steel on mechanical properties of welding in the presence of hydrogen was investigated. According to studies conducted, due to the charge of hydrogen, the hardness of base metal (BM) increased by 10%, the hardness of heat affected zone (HAZ) samples increased by about 13%, the yield strength of base metal increased by an average of 5% and the yield strength of HAZ increased by about 7%, indicating hardening. Elongation was reduced by 32–70% and the percentage of ductile fracture decreased by an average 46% which shows that the fracture of samples in the presence of hydrogen is brittle. In the study of hydrogen defect and concentration of hydrogen permeated to the material it was determined that, the ferrite-pearlite banded microstructure of base metal has a higher hydrogen defect sensitivity than HAZ with an acicular ferrite microstructure and hard phase. In base metal samples under various rolling conditions, the two-pass rolled and the final rolling temperature of 800 °C sample (2BM800), with a smaller grain microstructure and higher interface, had the most diffusive hydrogen content and therefore had the highest hydrogen defects. In the case of HAZ samples, the effect of hydrogen on the increase in hardness and strength properties is greater than that of the base metal samples due to the different microstructure (of the acicular ferrite) and the variable grain size (i.e. the presence of two coarse-grained and fine grained areas). Overall, the results of this study showed that the microstructure has a significant effect on mechanical properties, the amount of diffusive hydrogen and hydrogen defects in welds.

Study of Shrink Fitting for Shaft Couplings by Laser Heating

Laser shrink fitting for pipe coupling was developed as an application of laser forming. The coupling of the pipe of stainless steel and bar of hardened oxygen-free copper is made by laser shrink fitting. A bar is inserted into a pipe, and the pipe surface of the bar-inserted-part is irradiated and heated by 1kw class laser. Metallographic structure of the laser irradiated part of the pipe is not changed. Metallographic structure of the bar is changed into recrystallization structure. The fitted part of the pipe is shrunk in both circumferential and axial direction. The residual stress on the surface of the fitted pipe is compressive in both circumferential and axial direction. The tensile strength of the fitted part is 53% to the tensile strength of base metal of hardened oxygen-free copper bar.

Friction stir girth welding between aluminum and steel rods

Friction stir welding is enable to fabricate dissimilar materials joint which is difficult for conventional fusion welding. Thus, the method is promising way to fabricate multi-material structure for achieving weight reduction and high functionalization. Lap welding with spot weld (0D shape), butt welding with linear weld line (1D shape) and curved weld line (2D shape) were achieved for dissimilar welding between aluminum and steel. From the study, the shape change of weld line influence on heat input, material flow, and the process window of welding. The weldability with 3D shape weld line was investigated by friction stir girth welding between aluminum (AA6063) and steel (S45C) rods with 53 mm in diameter. It was difficult to fabricate defect free weld by friction stir girth welding without tool tilt angle. However, defect free weld was fabricated by friction stir girth welding with tool tilt angle. From the observation of material flow in the weld by X-ray CT, optimum material flow is generated in the weld. During welding, welding force and temperature increased with rotation of weld materials. These affected to the microstructure of weld with increasing the area of HAZ and softening the microstructure of weld. Fracture strength was 63.5 kN, and weld strength was about 117 N/mm2 and slightly lower than the strength of base metal.

Failure mechanisms and fatigue strength reduction factor of a Cr-Ni-Mo-V steel welded joint up to ultra-long life regime

It is known that welded joint is much “weaker” than base metal due to discontinuities of geometry, materials and residual stresses. It seems current international design rules do not adopt a uniform approach to weld efficiency, which is often defined as the ratio of the strength of a welded joint to the strength of base metal, in their guidance for creep and fatigue design of welds. This appears to be a great barrier for the application of nuclear welded structures which has a prolonged design lifetime of 60 years. In this work, fatigue strength reduction factor of a Cr-Ni-Mo-V steel welded joint, machined from welded steam turbine rotors for nuclear power plant, was investigated by performing axially push-pull cyclic loads tests with both cross-weld and pure base metal specimens up to very high cycle fatigue regime under ultrasonic frequency at ambient temperature. The effects of residual stress, strain localization, and microdefects in mismatched steels on failure mechanisms of welds were discussed thoroughly. Results show that fatigue strength reduction factor is varied in the range of 0.95-0.975, and is found to be dependent on fatigue lifetime for the first time. It is indicated that variation of fatigue strength reduction factor are associated with transition of crack initiation from specimen surface in high cycle fatigue regime to interior micro-defects in very high cycle fatigue regime. Comparing existing codes and standards for fatigue design of welds with experimental data indicates the over-conservativeness of present code-based design method. This implies a micro-defect based fatigue design approach is required for long life safe and reliability of weldments.

Mechanical Properties and Microstructural Characteristics of Friction Welded Dissimilar Joints of Aluminium Alloys

Joining of similar and dissimilar combinations of aluminium alloys 2024 and 6061 were performed using friction welding technique. Microstructure, hardness and tensile properties of the joints were characterized. Microstructure of the alloy were found to change significantly across the joint such as fully deformed, partially deformed and undeformed regions due to deformation, frictional heat and alloy characteristics. Extensive fine grain size was observed in the fully deformed region and volume fraction of finer grains was higher in the alloy 2024 as compared to alloy 6061. Hardness was lower in the weld interface region of the similar joints of AA2024 and AA6061. The lower hardness in the dissimilar metal joint was observed in the Heat Affected Zone(HAZ) of alloy 6061.The tensile strengths of the similar joints were 80% and 85% of respective base metal of alloys 2024 and 6061.The strength of the dissimilar metal joint was observed to be similar to the base metal strength of 6061 alloy. Tensile fracture occurred in the region of joints where lower hardness was observed. The maximum elongation were obtained in dissimilar joints of alloys and characterized by scanning electron microscope, it revealed that deep dimple pattern rather than that observed in similar joints.

Investigation on Microstructure, Micro-segregation and Mechanical Properties of Gas Tungsten Arc Weldment of Alloy 600 by ERNiCrMo-10

The present study investigates the Microstructure, Microsegregation and Mechanical Properties of alloy 600 fabricated by Gas Tungsten Arc Welding technique with ERNiCrMo-10 filler wire. Optical and scanning electron microstructure was carried out to evaluate the microstructural changes in the fusion zone. EDS analysis was conducted to assess the microsegregation of alloying elements in the fusion zone. Strength and toughness of the weld joint were assessed by tensile and impact test. The results show that the presence of cellular structure in the fusion zone. EDS analysis revealed the Mo-rich M23C6 carbide phases in the interdendritic regions of the fusion zone. Strength and toughness of the weld joint improved 1 and 58% compared to the base metal strength and toughness. The presence of M23C6 improved the strength and toughness of the weld joint.

Welding of Al-Mg aluminum alloy to aluminum clad steel sheet using pulsed gas tungsten arc process

Al-Mg aluminum alloy was lap joined to aluminum clad steel sheet using pulsed gas tungsten arc welding process and Al-Si filler metal. The effects of the welding heat-input were investigated on the joint microstructure and mechanical properties. Weld metal microstructure, formation of intermetallic compounds (IMCs) at the joint interface and the fracture locations were studied using stereo, optical and scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectroscopy (EDS). The joint strength of the welds was evaluated by shear-tensile test. The results showed that presence of a thin aluminum clad layer with 350 μm thickness drastically decreased the Al-Fe intermetallic thickness at the weld seam/steel interface to less than 2.5 μm. The joint strength increased with enhancement of the heat-input up to an optimum value and then decreased beyond it. This behaviour was justified in the light of the contradictory effects of the weld metal microstructure and adhesion of the weld metal to the aluminum clad layer near the weld root. In the optimum heat-input of 250 J mm−1, the joint strength reached to ∼90% of Al-Mg aluminum base metal strength. In all the welds, fracture path had an angle of 75 ± 3° with respect to the horizontal base plane. Stress analysis in the weld showed that fracture in the joint was controlled predominantly by the maximum normal stress rather than the maximum shear or von Mises effective stress.

Effects of natural aging and heat treatments conditions on mechanical properties of dissimilar composite between 6061 Al alloy and Al-Si12CuNi (AC8A) Al cast alloy fabricated by friction welding

This paper describes the effects of natural aging and heat treatments conditions on mechanical properties of dissimilar composite between 6061 Al alloy (AA6061) and Al-Si12CuNi (AC8A) Al cast alloy, which was fabricated by friction welding. The dissimilar composite was composed of specimens with the pipe part which had an outer diameter of 30.0 mm and an inner diameter of 24.0 mm. This composite had the softened region at the adjacent region of the interface of both materials. The softened region of both sides of the composite recovered the hardness with increasing natural aging time, and those with a natural aging time of 35 days (1 month) or longer had almost similar softened region. Then, the composite with a natural aging time of 35 days (AW composite) had approximately 62% in the tensile strength of the AC8A base metal. The fractured point was the adjacent region of the interface at the AC8A side, i.e. the softened region. The softened region of AW composites, which were re-treated with T6 condition of each base metal, was also recovered. Those composites had approximately 58% in the tensile strength of the AC8A base metal, and those fractured from the corner part of the inner diameter in the AC8A side. In addition, the composite with the high temperature environment with a heating temperature of 473 K, which was re-treated with T6 condition of the AC8A base metal, fractured from the corner part of the inner diameter in the AC8A side. That is, the interface of the composite tightly joined. The possibility that can use the composite fabricated by friction welding as an engine piston was obtained by experimental approach, because the composite did not have the fracture from the interface.

Effect of FSW parameters on microstructure and mechanical properties of AM20 welds

ABSTRACTThis paper aims to demonstrate the successful friction stir welding (FSW) conditions of AM20 magnesium alloy. The maximum yield strength and ultimate tensile strength of weld were found to be 75% and 65% of the base metal strength, respectively. The maximum bending angle of the welded joint was 45°. Observations revealed that less plunging depth, high shoulder diameter, and low tool rotational speed and welding speed give better tensile properties. Maximum temperature was observed at 1 mm away from the tool shoulder toward the advancing side. Micro-hardness variation is found to be decreasing along the depth of the weld, and nugget zone (NZ) gives the higher hardness values when compared with base material (BM) and other welded zones. Needle-like grains of the BM became equiaxed grains due to grain recrystalized by the FSW process. The grains in the NZ were finer than thermo-mechanically affected zone and almost same size of grains observed at bottom, middle, and top of the NZ.

Analysis of SiC nano-powder effects on friction stir welding of dissimilar Al-Mg alloy to A316L stainless steel

In this work, dissimilar friction stir welding (FSW) of an Al–Mg alloy (AA5083) to austenitic stainless steel (A316L) by using nano sized SiC reinforcement was examined. Two optimized traverse velocities of 16 and 20mm/min (and a constant rotational speed of 250rpm) with the intact joint appearance were considered for investigation the effect of number of passes on microstructural and mechanical properties. Microstructure of the single-pass FSWed specimens containing reinforcements indicated large steel fragments and agglomerated SiC particles within the stir zone (SZ). Further FSW passes led to more homogenous distribution of SiC particles and steel fragments. Field emission-scanning electron microscopy (FE-SEM) and energy-dispersive X-ray spectroscopy (EDS) were employed to analyze the in situ reactions at the joint interface and stir zone of Al-Mg alloy. No marks demonstrating the formation of tunneling defects were revealed at the stir zone up to six passes. Furthermore, streaks of tiny intermetallic particles together with steel fragments aligned in the direction of material flow. Tensile tests indicated that after six passes of FSW at traverse velocity of 16mm/min, the joint strength ratio to the ultimate tensile strength (UTS) of the AA5083 base metal (BM) was boosted up to ∼94 %, with an elongation reduction to 3% and a Vickers hardness enhancement of 250% in the stir zone.

Analytical Study on Microstructure and Mechanical Property in HAZ-Softened Weld Joint with High Heat Input of Low Carbon TMCP Steel

Three types of low-carbon TMCP steels with different strength of the same carbon equivalent were welded by the flux-cupper back for SAW(FCB) method in this work. The microstructure, hardness and tensile strength of the FCB welded joints were studied. Softening phenomenon occurs in the heat affected zone of low-carbon content and low carbon-equivalent TMCP EH36 steel after high heat input welding. The softened zone is mainly depended on the strength of the base metal (BM), which appears on the fine-grain zone and incomplete crystallize zone of BM with relative low strength, and on the coarse grain zone of BM with high strength. The ratio of the tensile strength between each FCB joint and BM is the same of 0.98 as the same carbon and carbon equivalent content of 0.5% and 0.315% of BM, which is almost independent of the strength of BM. The tensile strength of the incomplete crystallize zone depends on the strength of the BM, which results in the improved strength of the whole softened zone with the increasing strength of base metal.

Effect of pre and post welding heat treatment in SiC-fortified dissimilar AA6061-AA2024 FSW butt joint

The present study focuses on the effect of pre and post welding heat treatments on microstructural and mechanical properties of SiC included Friction Stir Welded joints in AA6061 and AA2024 aluminium alloys. The annealing of base metals as a pre welding heat treatment leads to more uniform distribution of SiC particles in the weld nugget. The post welding artificial aging heat treatment results in joint strength near AA6061-T6 base metal strength. Besides, the pre annealing and post aging heat treatment result in tensile strength and toughness of 92 and 96% of AA6061-T6 tensile strength and toughness, respectively. The micro SiC reinforcement in the weld nugget results in at least 14% higher weld strength than joints post weld heat treatment and without SiC particles additive. The abnormal grain growth in the weld nugget after post welding heat treatment has negligible effect on joint strength.

Optimization Analysis of Process Parameters of Friction Stir Welded Dissimilar Joints of Aluminium Alloys

Friction stir welding (FSW) is one of the new technique for welding materials in solid state welding process. In this proposed work we are using FSW to join the two dissimilar alloys of aluminium. The 6mm thick aluminum plates of aluminium 5086 and aluminum 7075 plates are considered for welding. These have been considered due to their application in various fields. In this experimental process Taguchi’s L9 orthogonal array method is used for optimizing the three process parameters namely rotational speed, axial force and welding speed. To produce a better joint the tensile strength is predicted for the optimum welding parameters and also their percentage of contribution is calculated, by applying the effect of analysis of variance. Depends upon the experimental study, the rotational speed is found better over the other process parameters, which enhances the quality of the weld. The tensile strength has been found for the optimum parameters and the result found during the experiment was 290Mpa which was higher than the base metal strength of aluminium 5086 alloy. The SEM fractograph analysis was done on the optimum parameters welded joints to show the fracture behaviour of tensile test which justifies the visual inspection results of brittle and ductile failures.

Mechanical Properties and Microstructural Characteristics of Friction Welded Dissimilar Joints of Aluminium Alloys

Joining of similar and dissimilar combinations of aluminium alloys 2024 and 6061 were performed using friction welding technique. Microstructure, hardness and tensile properties of the joints were characterized. Microstructure of the alloy were found to change significantly across the joint such as fully deformed, partially deformed and undeformed regions due to deformation, frictional heat and alloy characteristics. Extensive fine grain size was observed in the fully deformed region and volume fraction of finer grains was higher in the alloy 2024 as compared to alloy 6061. Hardness was lower in the weld interface region of the similar joints of AA2024 and AA6061. The lower hardness in the dissimilar metal joint was observed in the heat affected zone of alloy 6061. The tensile strengths of the similar joints were 80 and 85% of respective base metal of alloys 2024 and 6061. The strength of the dissimilar metal joint was observed to be similar to the base metal strength of 6061 alloy. Tensile fracture occurred in the region of joints where lower hardness was observed. The maximum elongation were obtained in dissimilar joints of alloys and characterized by scanning electron microscope. It revealed deep dimple patterns unlike what was observed in similar joints.

Al/Cu Dissimilar Friction Stir Welding with Ni, Ti, and Zn Foil as the Interlayer for Flow Control, Enhancing Mechanical and Metallurgical Properties

This research investigates the effects of Ni, Ti, and Zn foil as interlayer, inserted between the faying edges of Al and Cu plates, for controlled intermetallic compound (IMC) formation. The weld tensile strength with Ti and Zn as interlayer is superior to Al base metal strength. This is due to controlled flow of IMCs by diffused Ti interlayer and thin, continuous, and uniform IMC formation in the case of Zn interlayer. Improved flexural stress was observed with interlayer. Weld microhardness varied with different interlayers and purely depends on IMCs present at the indentation point, flow of IMCs, and interlayer hardness. Specimens with interlayer failed at the interface of the nugget and thermomechanical-affected zone (TMAZ) with complete and broken three-dimensional (3-D) grains, indicating transgranular fracture. Phase analysis revealed that Al/Cu IMCs are impeded by Ni and Ti interlayer. The minor binary and ternary IMC phases form adjacent to the interlayer due to diffusion of the material with Al/Cu. Line scan and elemental mapping indicate thin, continuous, and uniform IMCs with enhanced weld metallurgical and mechanical properties for the joints with Zn interlayer. Macrostructural analysis revealed IMC flow variations with and without interlayer. Variation in grain size at different zones is also observed for different interlayers.

Effect of treatment in weld surface on fatigue and fracture behavior of titanium alloys welded joints by vacuum electron beam welding

The effect of treatment in weld surface on four-point bend fatigue properties and fracture characteristic of Ti–6.5Al–2Zr–1Mo–1V alloy by vacuum electron beam welding were tested and analyzed. When the excess weld metal and excess penetration are removed, the high fatigue strength of joints can be obtained. When the excess weld metal and excess penetration were not removed, the fatigue strength of joints is about 40% of yield strength of base metal. Two kinds of fatigue crack initiations can be observed under the upper surface of joint, which show the obvious local tearing fracture morphology and bulk inclusions or compounds morphology.

ПРЕЦИЗІЙНЕ ЗВАРЮВАННЯ ТИСКОМ АЛЮМІНІЄВИХ СПЛАВІВ

Urgency of the research. Aluminum alloys are widespread materials in constructions of different branches of industry. Apart from ensuring the strength of permanent joints in typical units of constructions, their production requires to retain their designed form.Target setting. Precision joining of aluminum alloys by pressure welding is complicated owing to their high thermoplastic properties, heat- and electro conductivity. It requires the search of effective methods for obtaining products with low deformation level.Actual scientific researches and issues analysis. One of perspective joining methods of aluminium alloys is precision electric resistance welding through intermediate layers of aluminium foil. Their application promotes to localization of heat energy in the contact of welded components and decrease of product deformation level.Uninvestigated parts of general matters defining. Heat release process in the contact of welded components during electric resistance butt-welding of aluminum alloys through interlayers remains unstudied.The research objective. Aim of this paper is the development of precision electric resistance welding of aluminium alloys.The statement of basic materials. The investigation of heat release process has been carried out by estimated way with using of finite-element modeling. The joining of aluminum alloy 6063 has been realized by electric resistance butt-welding through intermediate layers of aluminum 1050 foil by thickness 11 μm. Welding conditions: the current density 300 A/mm2, the specific pressure 8 MPa, the welding time 0.5‑0.7 sec.Conclusions. It is shown, that quantity of heat generated in the contact zone during electric resistance butt-welding depends on number of layers in the interlayer. It has been determined that welding of aluminum alloy 6063 under offered conditions through 6 layers of aluminum foil allows to obtain welded joints with strength by 95 % from base metal strength and deformation level up to 2 %.

現場溶接型梁端仕口ディテールが先組みビルトH梁を用いた柱梁溶接接合部の変形能力に及ぼす影響に関する実験的研究

This paper deals with beam-end details of non-scallop method for field welding. The welding position of the lower flange in field welding is downward, the scallop construction method is generally used as the non-scallop construction method is difficult. The stress concentration occurs at the bottom of scallop, therefore brittle fracture of the beam end flange from the bottom of scallop is frequently reported. For that reason, joint types for preventing premature fracture from the bottom of scallop have been proposed. For example, those are horizontal haunch method, perforated flange method, etc. However, these joint types show sufficient deforming capacity, but in many cases volume of steel and processing cost increase. The purpose of this study is to propose welding non-scallop construction method filling the holes of scallops in field welding in order to eliminate stress concentration at bottom of scallop by changing the shapes of scallop parts. In this paper, filling welding construction method and inserting fillet construction method are used. It is clarified beam end details that improve deformation capacity of field welding beam-to-column joint with pre-built-up H-shaped beam. Full scale tests were carried out. The results obtained here are shown below. 1) Method to fill a column and the gap of beam-web by using welded joint (BM_L_W specimen, shown in Fig. 1c-3)) and to weld fillet weld diaphragm and billet (BS_P65 specimen, shown in Fig. 1b-2)) were most suitable as beam-end details improved deformation capacity of beam-to-column connections with field welding. 2) Cumulative plastic deformation ratio (shown it as follows with ηs) of BM_L_W specimen was 8.2, and the value of ηs exceeded deformation capacity of shop welding non-scallop method (shown in Fig. 13). Also, rate of increase in strength (shown it as follow with α) of BM_L_W specimen was 1.48. When it consider the restriction effect by diaphragm, strength of beam-end flange fracture reached tensile strength of base metal. From this, the stress concentration in a scallop bottom disappeared, and fracture origin shifted to end-tab. 3) ηs of BS_P65 specimen was 6.4, and at the same level as deformation capacity of shop welding non-scallop method (shown in Fig. 13). A of BS_P65 specimen was 1.40. As well as BM_L_W specimen, strength of beam-end flange fracture to the same level as base material toughness. 4) Deformation capacity of beam-end details which stress concentration remained behind in scallop bottom (BS_P50, BM_F and BM_L specimens) decreased in comparison with its BS specimen (shown in Fig. 13).